This invention relates to a method for determining mechanical properties of coating arrays. More particularly, the invention allows for the characterization of elongation and cracking of small-size coatings arranged in an array format.
Elongation properties of a coating material are of importance for automotive, telecommunication, and other applications. Conventional methods of elongation measurements involve the use of a large size coating material of about 100 mm in width and 150 mm in length, application of a conical mandrel test apparatus followed by a visual inspection of crack formation and measurement of the distance from the farthest end of the crack to the small end of the mandrel. The disadvantages of this standard method are the need to use a large coating area to obtain measurable parameters, manual measurements, difficulties in evaluation of several coatings simultaneously, and low sensitivity of measurements. A variety of test methods for elongation have been reported. These include the use of a CCD camera to measure the distance between the grid lines and calculate the elongation, automatic tensile test devices, devices to measure elongation due to bending under load, the use of lasers for noncontact elongation measurements and for the enlargement of the measuring range of speckle measuring systems of elongation.
Unfortunately, these techniques do not provide the capabilities for measurements of a large number of small-size coatings. What is needed are devices and methods for determining a variety of mechanical properties of multiple coating arrays. Such applications are of interest in combinatorial development of coating formulations and coatings.
The present invention solves the above-described problems by providing methods for testing elongation and cracking of coating arrays. In one embodiment, the method comprises simultaneously applying an elongating force to each of a plurality of coatings, and monitoring for a decrease in coating thickness and/or for cracks in each of the coatings. A relative performance characteristic of each coating is then determined based on a correlation between a measured decrease in coating thickness and/or a detected crack, and the corresponding force.
In another embodiment, the method comprises applying a plurality of coatings to a plurality of substrates wherein each coating is applied to a different substrate. The substrates are secured in a test arrangement and a force is applied to the substrates in order to bend the coating on each substrate. A detection system is then used to visualize cracks in the coatings and/or any decrease in coating thickness.
In still another embodiment of the present invention, the substrates are made of a deformable material. The substrates are preferably in the form of a geometrical shape having a curved surface. The force applied to the substrates modifies the shape of each substrate, thereby causing the coating on the substrate to bend and produce cracks. A detection system is used to visualize the cracks in the coatings and/or a decrease in coating thickness.
A further embodiment comprises applying at least one coating to a substrate, and forming the substrate into at least one coil having a specific diameter. A detection system is then used to visualize any cracks in the coating and/or a decrease in coating thickness.
Further aspects and advantages of the present invention will be more clearly apparent to those skilled in the art during the course of the following description, references being made to the accompanying drawings which illustrate some preferred forms of the present invention and wherein like characters of reference designate like parts throughout the drawings.